The present invention relates to a device and a method for controlling firing circuits for restraining devices.
In air bags, integrated switching circuits for controlling firing circuits are already being used, wherein single bits in a firing command control single transistors in output stages. Firing commands that are not recognized are ignored, and there is no reaction.
The device according to the present invention and the method according to the present invention for controlling firing circuits for restraining devices have the advantage, compared to that, that by using a bit combination, each controllable transistor is clearly identified, as a result of which a bit error does not create false signals by mistake. When a bit error occurs, the error recognition of the firing control recognizes it and notifies the processor. It is also of advantage that a faulty processor cannot release all output stages because of the inhibiting inputs present for the plus and minus output stages and the corresponding enabling commands. Beyond that, it is of advantage that the firing current is now clearly measurable, so that, on account of that, a notification on the functionability of the restraining devices is possible. The switchover between a pulse operation and a continuous operation of the output stages also leads to a higher firing speed or rather, higher firing efficiency.
It is of particular advantage that the element for measuring the firing current registers a current of a reference current source in connection with the adjustment information to a predefined desired current in a plus output stage, in each case, and stores the respective measuring result in a firing current register, so that this measuring result can then be transmitted to a crash recorder. The current source is, for instance, a current mirror in the plus output stage. In lawsuits, the record of the firing circuit""s activity is of advantage as proof. Furthermore, measuring the firing current to determine the firing energy is of advantage since, when the minimum firing current is known, the minimum firing energy can be calculated from this firing current, the resistance of the firing circuit and the firing time. This, then, makes possible intelligent energy management for the purpose of switching off the output stage transistors for firing of the firing element as soon as these are no longer needed, that is, when the minimum firing energy has already been reached. That also means that a smaller capacitor can be used as energy store for the energy reserve.
In addition, it is of advantage that the firing circuit control sends an error message to the processor, if a faulty bit combination was received, which activates no transistor, so that the processor can react accordingly, and can check its own functionability. This increases the safety of the whole system.
Again, it is of advantage that a switchover between pulsed operation and continuous operation of the output stages is carried out as a function of the energy reserve voltage, at high voltages high current firing being carried out, namely using pulsed operation, and this increasing firing efficiency and firing speed. The firing efficiency increases based on the higher voltage at the firing element, brought on by the high current firingxe2x80x94at simultaneously lower voltage drop at the output stage. In the case of currently used pyrotechnical firing elements, the triggering time decreases rapidly with increasing firing current, whereby firing speed is raised. Using pulsed operation, the plus output stage becomes short-circuit-resistant to short-circuit to ground, since from the pulsing at the output stage transistor only a limited power is created, which is smaller than that which is maximally permissible. Beyond that, in pulsed operation it is possible to have higher firing currents without thermal overload of the plus output stage. In addition, the area of the plus output stage on an integrated circuit can be made smaller.